Magnetite nanoparticles were modified to render them suitable for bio-applications, namely drug delivery and hyperthermia, using two different approaches. The first approach is to graft polymers onto the nanoparticles using surface-initiated atom transfer radical polymerization, followed by chemical linking of biomolecules such as heparin and doxorubicin onto the grafted polymers. The monomers used include N-isopropylacrylamide, N-vinylformamide and methacrylic acid. It was found that the heparinized nanoparticles could reduce macrophage uptake, and at the same time inhibit plasma clotting. The doxorubicin-bearing nanoparticles were able to release a greater amount of the drug under acidic conditions as opposed to physiological pH, and could potentially serve as drug depots. The second approach was to encapsulate these magnetite nanoparticles into polypyrrole nanospheres via emulsion polymerization for potential use as hyperthermia causing agents. After functionalization, the nanospheres can target cancer cells in vitro and possess good magnetization which is useful for magnetic fluid hyperthermia.